1. FIELD OF THE INVENTION
The present invention relates to pressure-relief valve devices particularly for use with hydraulic mining equipment, such as props or rams.
2. DESCRIPTION OF PRIOR ART
Pressure-relief valve devices of various designs are widely used to protect mining equipment against excessive pressure and especially hydraulic props which are exposed to high forces by the roof of a mine working. Known devices are of small compact design and function to connect with a working chamber of the mine equipment so as to be exposed to the pressure fluid therein. Under normal conditions the valve of such a device remains closed but excessive pressure will cause the valve to open to permit pressure fluid to flow through the device and escape to relieve the excess pressure.
Valve devices of the aforementioned kind are usually embodied as cartridges with a hollow sleeve containing a spring and a guide screwed into the sleeve. A part-hollow valve member guided for displacement by an axial bore in the guide is exposed to the spring force to maintain closed a valve established between openings in a stem of the valve member and an O-ring seal. The spring force can be transferred to the valve member with the aid of a shaped disk or pressure piece and a connector part can serve to mount the device to the equipment to be protected. Examples of known devices are described in U.S. Pat. No. 4,284,101, German patent specification Nos. 3420890, 3245667, 3018145, 3508986; European patent specification No. 0096303 and in commonly assigned U.S. Pat. No. 4,716,928, the disclosure of which is herein incorporated by reference. In some prior art designs, where the connector is provided, this is either integral with the guide or not readily removable therefrom except upon wholesale disassembly of the valve device.
A general object of the invention is to provide an improved valve device.